Method and means for recording sound



a- 8 1 .4 14a. WALKER "2,293,229

union ,mn .umms ron nnqoapme scum) filed EJ111117. 1940 INVENTOR. JOSEPH B. WALKER 1 fl/W W ATTORNEY.

phone."

Patented Aug. 18, 1942 OFFICE mz'monann MEANS ronnaconnme sormn Joseph B. Walker, m Angeles, Calif. Application July 17, 1940, Serial No. 345,941 20 Claims. (01. its-100.2)

My invention relates generally to the recording of sound and more particularly to its recording by magnetic means on a steel tape or wire.

The fundamental principles underlying this system of sound recording have been known for a number of years, and apparatus making use of this system is generally known as the telegra- In one adaptation of the telegraphone, a continuous loop of tape has been used so that the message may be repeated over and over again. as in' advertising displays. For other uses the tape supplied from one real or spool passes through the recording or reproducing deviceand is then wound upon a take-up spool. In this lattersystem, it is necessary to rewind the-tape before the sound first recorded may be 'reproduced. Since the tape is of small size, a high rewinding speed is likely to and often does break itrwhile if a slower speed is used, the delay between recording and reproducing becomes objectionable. This is one of the principal reasons why the telegraphone has not found commercial success as an oflice dictating machine.

It is, therefore, a major object of my invention to provide a method and a means utilizingthat method of recording sound on steel tape in Fig. 2 is a sectional view taken at 2-2 in mg. 1,

Fig. 3 is a plan view of the recording magnet taken at 3-4 inFig. 2,

.Fig. 4 is an elevational view of the recording magnet taken at 4-4 in Fig. 3, and

Figs. 5a, 5b, 5c, and 5d are cross-sectional views 0! dlflerent styles of tape which may be used'to t advantage in my device.- 1

In" the operation of such recording devices, a tapeoi steel or other magnetic retentive material is passed between the poles or an ele c tromagnet which, when sound is being recorded, is energized by currents varying in frequency and amplitude in accordance with 'sound waves. This varying current creates a agnetic held of varying strength which passesthrough the steel as a result, the steel tape is locally magnetized in proportion to the strength of the magnetic netic fluctuations impressed upon it. It will be,

apparent, of course, that it is possible to secure 1 satisfactory results if the tape is passed by only one pole of the electromagnet, the lines of magnetic flux being allowed to return to the other pole over any possible path, and it is to be imderstood that in the specification and claims where I speak of the tape being between the poles of the electromagnet, I mean'to include the case in which the tapeis adjacent to only a single pole oi the magnet. a

. If this magnetized tape bearing a sound record thereon is now passed between the poles of a suitable electromagnet, the magnetic variations will be transformed into electric variations (1. e., a'fluctuating electric current) by. electromagnetic induction as is well-known in the art, this operation being usually known as picking up" the sound. It is customary to use the same e1ect-ro-' magnet for both recording and reproducing the sound, since this requires less equipment and the change maybe accomplished by merely altering the connections slightly. After the sound record made. it may be erased by polarizing the tape by passing it adjacent to the pole or poles of a permanent magnet, or of an electromagnet energized by direct current. The eras- :5 ing may be done by a separate magnet or by' the magnet used for recording the sound by connecting it to a sourcevof direct current. The electromagnet used in the recording and reproducing of the sound is connected to a circuit which forms 40 no part of this invention and which may be the customary recording and reproducing'circuit used in sound work and well-known to those skilled in the art. g

Referring now to the drawing, and particularly to Figs. 1-4 thereof, the numeral It indicates a smooth cylinder or drum. drivenby a motor l I, and connected thereto by suitable speed-reduction means l2. Mounted on the drum III is a I helically-lwound steel tape l3, shown ingreatly enlarged and Scale, which is particularly characterizedby being'edge-wound, i. e.. wound so that its smallest'dimension is parallel to the axis or the drum. By using an edgewound tape, the advantages of a wide tape are retape between the'poles of the electromagnet; and 5 tained. and at the same time enough tape to record sound for a considerable length of time may be carried on the surface of a relatively short drum, while permitting he whole of thetape to be immediately availabl at-any time.

Obviously, to provide the greatest length oftape possible along the length of the drum, the

tape should 'be closely wound so that the outeredges of the turns present a substantially smooth cylindricalsurface; but when this is done, there is of course no space available between the abutting-turns, to allow the poles of the magnet to along rod I5, and the two carriers may connectedtogether by suitable means such as a yoke is. In this way,-when the magnets -ll-and .la

are moved along the length of the cylinder ll, I

the separator 22 will be moved along with them,

and will thus reduce the side strain on the magnet to a minimum.. This form of separator means cooperates in a most satisfactory manner "with the tape l3, for the latter rotates as a firm,

placed on either side of the isolated turn of tape and to bear against its faces. To effect such separation, I provide suitable means such as a horizontal rod l5 extendingthe *length of the cylinder l0, on which is mounted a carrier H, rotatable about the rod as a center and carrying a pair of electro'magnets l6 and 16a.

solid unit while at the same time it is flexible and free at the-point of translation. If a separate magnet is to be used for erasing, the member 2| makes a very suitable place for it to be located. but in either event the separator 22 is a desirable, though not indispensable, member.

The electromagnets l6 and, lia are provided with pole pieces 23 and 23a, respectively, which extend-from the cores of the magnet to the op-' posite sides of the tape 13 and bear against the latter. .To take -care of any wrinkling or displacement of the tape, I prefer to pivot the magfnets l6 and Ilia at suitable points, such as 24 On the side of the carrier I4 nearest the drum l0 and extending downwardly therefrom, I providea pair of knife-like members I! and I'la'which are 'curved away from the drum l0 as shown best in Fig. 2 and which are tapered from a relatively thick portion near the point of .attachment to the carrier to a relatively thin portion at their lower end. When the carrier I4 is lowered from its raised position, the knife-like. members l1 and Na will enter in between adjacent turns of tape and separate them, leaving one turn in between Y the knives'to be engaged'by the poles of the electromagnets l6 and 16a. While I prefer to provide the members l1 and- Fla with the tapered form just described, it will be apparent that the same results may be obtained if the knife-like members diverge upwardly from their lower extremities where they first enter between the adand in addition the tape must be wound loosely enough to permit it to slide along the drum, while at the same time being wound tightly enough to I prevent unnecessarymovement thereof. To aid in maintaining the separated tape in a proper spaced relationship, I preferably provide an additional guide member I 8 extending from above the electromagnet l6 and lia into the space formed by the knives l1 and lla. In the form shown, I have illustrated the guide ll as having an L shape with a bifurcated end which fits over' and engages the, isolated turn, with a prong fitting into the space on either side thereof.

Along the opposite side of the cylinder I 0, I may provide a rod 20, similar to the rod I 5, on

which is mounted a carrier 2| having a spacing member 22 attached thereto which is adapted to maintain the separation-of the turns of tape. In the form shown, the member 22 consists of an arm having a bifurcated end somewhat similar to that of member l8 and acting in the same way, but it will be apparent that other forms may be used as desired. The carrier 2| is rotatably .mounted on the rod 20 and may slide along the greatly enlarged scale.

latter in the samemanner that carrier l4 slides and 24a, respectively, and provide a spring 2' which urges the magnets andtheir respective pole pieces together. By providing handles 2! and 26a for the magnets, the pole pieces maybe easily separated so that the tape l3 maybe inserted between them, while thespring 25 insures that each pole piece will bear against the corresponding side of the tape with a pressure equal to that of the other pole piece.

As is well-known in the art, the farther the pole pieces are separated, the more the lines of magnetic flux will spread out. As a consequence, there is an overlapping of magnetic impulses which covers up the high frequency impulses and permits only the low frequency impulses to be distinguishedan effect which may be more thoroughly understood by referring to the art of recording and reproducing sound films wherein a very narrow window or slit is used to scan the sound track. Consequently, in magnetic recording, the high frequency tones. willbe recorded when a thin tape is usedbut will be lost if a thicker tape is used, assuming the lineal speed to be the same in both cases. I, therefore, prefer to use a thin tape and to have the pole pieces bear against said tape so as to secure high quality reproduction without requiring a high lineal speed in the recording or reproducing of :the sound.

With high grade Swedish steel, a tape thinner than .004 of an inch produces excellent recordings, but the physical strength of such a tape is so small as to render its use impractical, A tape .004 of an inch thick is the thinnest I have found to be practical, and one .006 of an inch thick produces good results, but above .008 of an inch the reproduction is .not so satisfactory, and there is a noticeable falling oil of the higher frequencies. However, the thinner the tape, the more difficult it is to handle and the more likely it is'to break; and to remedy this difliculty, I have found that the use of a tape having a thicker base portion with a thinner outside edge portion will both permit the recording of high frequencies and provide the necessary mechanical strength for the treatment normally accorded such recording devices.

In Figs. 5a, 5b, 5c, and 5d, I have illustrated four different forms of tape which may be used, all four figures being drawn to a distorted and In one form of device which I have used, these tapes areapproximately 54; of an inch high, .012 of an inch thick at'the recorded thereo thecarriers iil and Y rods al and 20 tbfthe desired position, where the carrier is then lowered, the knife-like meinterm n ing [Ila automatically segregating one "turn of the tape as they are lowered. The carrier base. and .004 of an inch thick at the top. the iormsshown. thoseinl'igsfiaand tdmay be iormed with perhaps the fewest number 01' operations. while those shown in Figs. 5b and to require more operations The triangular forms shown in Figs. 5cand 5d are the strongest and will stand the most abuse but the forms shown in Figs. 5a and so will give somewhatbetter quality of reproduction. 'This is especially true it a double passage 01. thetazpe between the pole pieces, to be described'later, fI-Iowever, for normal use, the increased strength and greater durabilityjor the iorims, and J 541 i-" 9313 3"? l' b j ih. 1W3? in qualitytiw With this termini 1 a idst device;- no: its

iary tmeansneed beprovided to move the recordinj krcl r dl nsmh i r i a m gnets, and'spac- 1 new separating members along the length. or cylinder; vHence}the carriers! .and li-ar'e designedto-slide ireelyon the rods II and a'nd'are joined jtogether -by the yoke it. so that they retainfthe'ir proper relationship .at all times;

'Withsuch'a;construction it will be seen that ny portion of thefentire sound record is instantvly available n WE the sound h s may be done by r i andsliding them along the is then loweredso that the arm 1-22 engages the: isolated turn, the -polepieces fl and 23a are adjusted to bear againstfitheiopposite,i'aces of I thetape ll, and th erasin fundersome circumst" While I have vshown and described apreferred :iorm oi myinvention, I do'not wish'tobelimleproducing, ,or ding'rnay proited to the particularfii'orm .or arrangement or parts herein described andshown, except insofar as covered by my appended claims. a I claim as my invention: 1 a

of an edgewound cylindrical helix formed of said tape; placing a pole of an electromagnet adjacent one of said turns of said helix; and rotating said helix about its axis as a firm solid unit while at the same time keeping it flexible and free at the point of translation, so that all of said tape may pass said pole.

3. A device of the character described which includes: a. cylinder; a helical edge-wound tape mounted upon the periphery of said cylinder, said tape being of a material having magnetic retentive properties; an electromagnet having a pole piece adjacent one face of a turn of said tape; and means for rotating said cylinder and helix.

4." A device of the character described which includes: a cylinder; a helical edge-wound tape mounted upon the periphery of said cylinder, said aacaaaa tive properties; means for mechanically separating any one of said turns ot-tape from the-others: an electromagnetihaving a .pole piece adjacent oneiace ot a turn or said tape: and means for rotating said cylinder and helix. I

5.A device volf the character described'wh'ich "includes: a cylinder; a helical edge-wound tape mounted onsaidcylinder'so as to be capable of being moved along the length thereof, said tape being or a material having magnetic retentive .propertiesrmeans for segregating any one of said turns oi tape from the others; an electromagnet having a pole piece adjacent one face or a turn or said tape; and means ior rotating said cylinder-"and helix. 7 r f 6. A device of the character described which includes: a cylinder; a helical edge-wound tape mounted upon said cylinder, said tape being of a material havingmagnetic retentive proper-. ties; means for segregating any one of said turns of tape irom the others, said means. including a a pair of pivotally-mounted knife-like members adapted to enter between adjacent turns and force them apart; an-electromagnet having a tape being or a material having magnetic reten- 7s pole piece adjacent one nee oi a turn of said tape; ,and' means for rotating said cylinder and helix. v I

7. A deviceioffth character described -WhlCh includes: a-cylindera ahelical edge-wound tape having a relativelythickbase portion and a relatively thin outer edge portion mounted upon said cylinder, said tape being of a material having magnetic retentive properties; means for segregating any one of said" turns of tape from the others; anelectro'magnet having a pole piece adjacent one face ,of a turn of said tape; and means] for rotating said cylinder and helix.

. 8. A.device ;,oi the character described which includes? a smooth cylinder of substantially uniform diameter; a helical edge-wound tape mounted 'on said cylinder, said tape being of a material possessing magnetic retentive properties, and being wound loosely enough on said cylinder to permit of its being moved along the length thereof; means for segregating one turn of said tape from the others; an electromagnet having a pole piece adjacent one side of said segregated tum? spring means urging said pole piece toward said turn; and means for rotating said helix about its axis.

9. A deviceas described in claim 8 in which the means for segregating said turn of tape includes a pair of pivotally mounted knife-like members adapted to enter, one on either side of said turn, between adjacent turns and force said turns apart.

10. A device as described in claim 8 in which said tape is provided with a relatively thick base portion and a relatively thin outer edge portion.-

11. A device of the character described which includes: a smooth cylinder of substantially uniform diameter; a helical, edge-wound tape mounted on said cylinder, said tape being oi a material possessing magnetic retentive properties, and being wound loosely enough on said cylinder to permit of its being moved along the length of said cylinder; supporting means parallel to said cylinder but spaced therefrom; carrier means pivotally and slidably mounted on said supporting means; an electromagnet mounted on said carrier means; knife-like members mounted on said carrier means and adapted to be inserted between adjacent turns of said tape to separate said turns, a pole piece of said electromagnet being adapted to bear against a lace of a turn of tape so separated from its adjacent turns; and means for rotating said helix about its axis as a firm solid unit, while at the same time-keeping it flexible and freeat the point of translation.

12. A device as described in claim 11 in which said tape has a relatively thick base portion adjacent said cylinder, and a relatively thin portion outwardly from said cylinder.

14. The method of recording and reproducing sound on a tape having magnetic retentive propertles which includes: separating adjacent turns of an edge-wound helix formed of said tape; placing a pole of an electromagnet adjacent one of said turns of said helix thus separated; and rotating said helix about its axis so that all of said tape may pass said pole piece, while simultaneously axially shifting one turn of said tape so that the separation of turns will move with said pole piece from one end of the helix to the other.

15. A device of the character described which includes: a cylinder; a helical edge-wound tape mounted upon said cylinder, said tape being of a material having magnetic retentive properties; means for separating adjacent turns of said helix; an electromagnet having a pole adapted to be placed adjacent one of said turns thus separated; and means for rotating said cylinder about its axis so that all of said tape may pass said pole piece, said helix being axially shiftable on said cylinder so that the said separation of turns will move with said pole piece from one end of the helix to the other.

16. A device of the character described which includes: a smooth cylinder of substantially uniform diameter; a helical edge-wound tape mount-- ed on saidcylinder, said tape being of a material possessing magnetic retentive properties, and being wound loosely enough on said cylinder to permit of its being moved along'the' length thereof; means for segregating one turn of said tapei'rom the others; an electromagnet having a pair of polajpieces adjacent the-slides ofsaid segregated turn; spring means urging said pole pieces to- I ward said turn; and means for rotating said helix about its axis. 17. -A device of the character described which includes: a cylinder; a helical edge-wound tape mounted upon the periphery of said cylinder, said tape being of a material having magnetic retentive properties; an electromagnet; means for placing a pole. offsaid electromagnet between adjacent turns of said tape and against a face of one of said turns; and-means for rotating said cylinder and said helix.

18. A device of the character described which includes: a magnetic retentive tape-edgewound in the form. of a cylindrical helix, the turns of which may be shifted axially of said helix; means for segregating any one of said turns of tape from the others; an electromagnet having a pole piece adjacent one face of a turn of said tape; and'means for rotating said helix.

19. A device of the character described, which includes; a magnetic retentive tape edgewound in the form of a cylindrical helix, the turns of which may be shifted axially of said helix; an electromagnet having a pole piece adjacent one face of a turn of said tape; and means for rotating said helix.

20. The method of recording and reproducing sound on a tape having magnetic retentive properties, which includes: placing a pole of an electromagnet adjacent one face of a turn of said tape edgewound as a cylindrical helix; and rotating said helix about its axis while at the same time axially shifting one turn of said tape so that the separation of turns remains adjacent said pole piece while all of said tape passes said pole piece.

JOSEPH B. WALKER. 

